Surfacing of materials



April 1966 I c. w. HIGHBERG 3,243,922

SURFACING' OF MATERIALS Filed July 9, 1963 5 Sheets-Sheet 1 GRINDING HARD ABRASIVE SEGMENTS GRITS 72 HOLDERS COOLANT DISCHARGE INVENTOR. CARLE W- HIGHBERG ATTORNEY April 5, 1966 c. w. HIGHBERG 3,243,922

SURFACING OF MATERIALS Filed July 9, 1963 5 Sheets-Sheet 2 II| FIG.6 L I 3;; I

I I SPINDLE l 32 l GRINDING I DIAMOND I *"E GRINDINGf g} SEGMENT38 COOLANT v SUPPLY. :f TANK 28 PUMP I 45 I IT-J: ORIFICE FOR I WHEEL 4e COOLAN'I\'5O 48 ORIFICE FOR 47 COOLANT 49 I I IIII'IHI GRINDING E 4: SEGMENT 52 DIRECTION OF COOLANT FLOW 45 COOLANT SUPPLY TANK 43 HARD ABRASIVE GROOVES GRITS GRINDING MATRIX INVENTOR.

CARLE W. HIGHBERG ATTORNEY April 5, 1966 c. w. HIGHBERG SURFAGING OF MATERIALS Filed July 9, 1963 MELTING FURNACEI PIC-1.8 I

I ANNEALING CHAMBER] K II INITIAL DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS DIAMOND GRINDING STATIONS ADDITIONAL SUCCESSIVE DIAMOND GRIND- ING STATIONS-HIGHER CONCENTRATIONS OF DIAMONDS THAN IN INITIAL STATIONS LATE DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS MATERIALLY LOWER THAN IN THE ADDITIONAL SUCCESSIVE STAGES IRON OXIDE POLISHING TRANSFER AND REVERSAL INITIAL DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS DIAMOND GRINDING STATIONS ADDITIONAL SUCCESSIVE DIAMOND GRIND- ING STATIONSHIGHER CONCENTRATIONS OF DIAMONDS THAN IN INITIAL STATIONS LATE DIAMOND GRINDING STATIONS LOW CONCENTRATIONS OF DIAMONDS MATERIALLY LOWER THAN IN THE ADDITIONAL SUCCESSIVE STAGES IRON OXIDE POLISHING 5 Sheets-Sheet 5 FIRST SIDE FTROCESSING SECOND SIDE faocsssmc I N VENTOR.

CARLE W.

HIGHB ERG ATTORNEY NE mm H 6 R0 I EE DR II MW. I 0

Filed July 9, 1963 5 Sheets-Sheet 4 MOTOR 24 FIG.9

III"

GRINDING WHEEL 2| 2 COOLANT TAN K 28 GLASS SHEET I5 FIG."

SEGMENT HOLDER n mN DE M G E S s G T mN E NM mm 63 DIRECTION OF WHEEL ROTATION DIRECTION OF WHEEL ROTATION GRINDING SEGMENTS S T N E M G E S GRINDING DIRECTION OF WHEEL ROTATION DIRECTION OF WHEEL ROTATION INVENTOR. CARLE w. HIGHBERG bis A ril 5, 1966 I c. w. HIGHBERG 3,243,922

SURFACING OF MATERIALS Filed July 9, 1963 5 Sheets-Sheet 5 INVEN CARLE W. HIGH A TTOP/UFYS United States Patent Jersey Filed July 9, 1963, Ser. No. 293,601 3 Claims. (Cl. 51-283) This is a continuation-in-part of my copending application Serial No. 193,925, filed May 11, 1962, which in turn is a continuation-in-part of my copending application Serial No. 119,444, filed June 26, 1961, now Patent No. 3,177,628, granted April 13, 1965.

This invention relates in general to the grinding of materials with hard abrasives, and more particularly, to a new and improved method and apparatus for grinding and/or honing of surfaces or edges of materials such as, for instance, glass, stone, ceramics, cemented carbides and ferrous metals.

In the prior art manufacture of plate glass, the plate glass is continuously extruded from the melting furnace, followed by passage through an annealing chamber. From the annealing chamber, the plate glass is subjected to grinding and polishing, typically involving passage first through twenty-eight successive beach sand grinding statons. The grinding operation is carried out at each of these stations by large grinding heads having vertically mounted spindles, which have horizontal grinding surfaces extending across the width of the plate glass. After the grinding at such beach sand stations, additional polishing is required, typically at forty-two additional stations, wherein the polishing heads also have vertical spindles, and iron oxide or rouge is employed as abrasive. This prior art process for grinding plate glass is disadvantageous for the reasons that a large amount of expensive machinery and floor space is required, and the facilities and manpower required for handling the bulky abrasives are very costly.

In my Patent No. 3,177,624, granted April 13, 1965, a division of my copending application Serial No. 50,352, filed August 18, 1960 now abandoned, a considerable improvement in the grinding and polishing of glass is provided by the replacement of the first two-thirds or more of such seventy stations of grinding and polishing with a lesser number, such as or less stations of diamond grinding. This large reduction in the number of grinding stations required was achieved by the use of diamond grits or particles in the surface portion of the grinding heads instead of the beach sand. This method is a considerable improvement for the reasons that the amount of floor space, machinery and manpower required in the processing of the plate glass is considerably re duced, with resulting reduced cost of the entire operation. In this improvement method, the diamond concentration in terms of carats per cubic inch of grinding wheel matrix is relatively low in the initial stations of rough grinding and is increased in the additional successive grinding stages and later stages with a corresponding reduction in diamond particle size, the diamond concentrations being the largest or highest in the late stages.

A further improvement in the grinding of glass over that of application Serial No. 50,352 is disclosed and claimed in my copending application Serial No. 119,444,

filed June 26, 1961. In the method of application Serial No. 119,444, diamond grinding of the glass may be carried out in initial stations with Wheels having a low concentration of diamonds of predetermined grit size, followed by diamond grinding the glass in additional successive stations with wheels having higher concentrations of smaller grit size diamonds than in the initial stations, and diamond grinding the glass in late stations with wheels having low diamond concentrations materially lower than those of the wheels of the additional successive stations and which can also be materially lower than the diamond concentrations of the wheels of the initial stations, the diamond grits of the wheels of the late stations being of still smaller grit size. The method and apparatus of this application achieve a striking economy in the quantity of diamonds required and a considerable reduction in overall costs as Well as a considerable prolonging of the life of the grinding wheel, reduction in breakage and damage to the glass, and obtainment of grinding results that are predictable and can be duplicated.

In a preferred embodiment of application Serial No. 119,444, the grinding wheels are segmented with the grinding segments being arranged on the wheel support in a generally circular arrangement preferably adjacent the peripheral edge portion of the support. The grinding segments each comprise a matrix having diamond grits bonded therein. More preferably the grinding segments are arranged on the wheel support in a continuous narrow arrangement with minimum spacing between neighboring segment edge portions. By reason of this circular arrangement of the segments on the wheel support, a considerably prolonged life of the wheel is achieved.

In accordance with the present invention, it has been found that the combination of (l) grooved grinding wheels, preferably radially grooved wheels with a metal matrix bonding the grits, (2) hard abrasive grits on these grooved wheels of preferably a grit size of 200-230 grit size or finer, more preferably within the range of 500 2500 grit size, and (3) liquid coolant supplied to the wheels during the surfacing resulted in a significant improvement in the surfacing of the plate glass at late stations of the grinding method of application Serial No. 119,444. Narrow grooves are generally used as will be specifically discussed hereinafter, relatively wide grooves having little or no advantage. Further, unnecessary width of grooves cuts down on the available grinding surface. This combination of the three features mentioned above of this invention significantly improved the plate glass surfacing at a variety of grit sizes within these ranges.

In the grit size range of 500-2500 grit size, grit sizes of the abrasive within the range of 1050-1500 grit size are especially preferred.

The grinding apparatus of this invention comprises a rotatable spindle, a grinding Wheel mounted on the spindle, means for rotating the spindle and hence the grinding wheel, and means for feeding plate glass through the apparatus for surfacing by the wheel. The grinding wheel comprises a support member, a matrix preferably of metal on the support member providing a grinding surface, and means for securing the matrix to the support. A plurality of spaced grooves are provided in the grinding surface, diamond grits or grits of other hard abrasive materials hereinafter disclosed and of the grit size previously disclosed are bonded in the metal matrix, and means are provided for supplying a liquid coolant to the wheel, preferably to its inner grinding edge.

The grooves employed are preferably radial; i.e. extending outwardly in radial fashion with the center of the wheel their origin if they were extended inwardly this extent. However, in addition to the radial grooves, one or more concentric grooves can be utilized, i.e., grooves arranged concentrically with respect to the center of the wheel and one another in the grinding surface. Concentric grooves may be desirable particularly where the grinding surface radial dimension is large and such concentric grooves would suitably intersect the radial grooves. The

grooves may be equally or substantially equally spaced in the wheel grinding surface and preferably extend from t the inner to the outer edges of the cutting surfaces.

-Width of the grooves is related to size of the abrasive gritsused. In general, the use of coarser abrasive grits requires greater width grooves and smaller size grits narrower width grooves. For instance, for 12 foot diameter wheels, grooves having width of preferably from about .005f'-.023" may be employed when grits of particle size of about 8-25 microns (1050 grit size) are used, and grooves of width of preferably from about .010.045

may be employed when larger size grits of particle size of.

about 30-50 microns (500 grit size) are used.

The grooves may be provided in the wheel grinding surface after the wheel has been made by any suitable method, such as by cutting by means of any conventional cutting tool well known to those skilled in the art, or by spacing the abrasive segments, usually present in wheels over 18-inch outer diameter, a sufficient distance when mounting same on the wheel holder to provide the grooves. Thus the term groove or grooves is used in a broad sense herein to include not only grooves provided in the grinding surface by cutting, gouging, etc., but also provided by spacing apart the abrasive segments the desired distance, or by the combination of cutting, gouging, etc., and the spacing apart of the abrasive segments.

The shape of the grooves is also an important consideration. V-shaped grooves as shown in certain of the embodiments of this invention may be used, but it is preferred to work with flat-bottomed grooves of uniform or substantially uniform width, since in such case the groove width does not change as the grindingsurface wears away.

While it is not definitely known why or how these grooves exert their beneficial eifect, one plausible explanation is that the grooves serve to aid in the removal of the abrasive debris from the wheel cutting surface. The presence of this abrasion debris has resulted in unsatisfactory results heretofore when wheels with 1050 grit size abrasives and a diamond concentration of 0.25. carat/ cu. in.

-were used. In fact, such wheels could not be operated even at nominal downfeeds without excessive burnishing of the glass. The cause of this difiiculty has been attrib- V uted to the lodging of abrasion or grinding debris on or contiguous to the cutting surface of the wheel. Further,

when 2500 grit size diamond wheels were used, the metal bond or matrix utilized actually became embedded. in the glass at nominal glass removals and no grinding could be intervals on the grinding wheel having the fine abrasive particles or grits in accordance with this invention results insuperior grinding wheel life, and'in superior. surface i finish of the material being. ground and polished. It also the wheel is such that it lowers the grinding life of the 7 wheel. In typical runs, grooves A inch in width were found advantageous in wheels with 200-230, 500 and 1050 grit size diamonds in wheels of 3-inch O.D. (i.e. outer diameter) and 30-inch O.D. However, in larger size wheels such asfor instance a 12-foot O.D. wheel with 15 00 grit size diamonds, grooves smaller than 1A inchand typically 0.009 inch in width are preferred.

The frequency of grooves required for optimum performance is also a function of the grit or particle size and the wheel size. For a given grit size, the number of .grooves required increases with the size of the wheel.

For example, with diamond wheels operated at about 2850 surface feet per minute, favorable grinding with 500 grit size diamonds was observed with 3-inch O.D. cup wheels containing four grooves each of A inch width and with 30-inch O.D. segmented wheels contain 'ing 96 grooves each of A inch width. The optimum frequency of the grooves for a particular wheel size increases with the decrease in particle-or grit size. For

instance, it has been found that with three-inch O.D. cup. wheels with inch width radial grooves, the optimum number of grooves was as follows:

Optimum number of grooves Grit size:

' with resultant loss of diamond life of the wheel.

Coolant is employed for absorbing heat from the grinding surface, which improves the life of the grinding wheel, and this coolant is preferably delivered or sup- .plied to the inner cutting edge of the wheel, such delivery of the coolant being of considerable importanceto the performance of. the diamond wheels. It was found that by reason of supplying the coolant to the inner cutting edge of the wheel, the; coolant is most efiiciently utilized in contrast to delivery of" the coolant to the outer 1 cutting edge of thewheel which gives less efiicient useof accomplished. However, the presence of the. grooves spaced preferably radially at equal or substantially equal the coolant; By the interior. delivery of the coolant, centrifugal force causes it to contact all the exposed diamond grit surface, provided the segments are placed with minimum spaces between them. However, particularly with large grinding wheels, it may be useful .also to apply coolant to the outer cutting edges. The coolant can be supplied to the inner cutting edge of the wheel by means of a hollow shaft spindle, or with larger 7 wheels preferably by fiowingdown theinner edges ofthe grinding segments through suitably disposed orifices or holes in the diamond wheel. The coolant is an oilin water emulsion-type and preferably comprises, by volu'me, from about 20-100 parts of water per each one part of coolant concentrate (oil and emulsifier).

For use withthe, coolant and grooves, wheels haying the diamond grits bonded thereto with metal are :preferred. 'Among these metal bonded wheels, a copper based alloy, i.e. an alloy containing a major proportion of copper is the preferred bonding material or matrix.

In addition to the copper, other metals advantageously present in the alloy of the bonding material or matrix include one or more of Zinc, tin, silver, aluminum, beryllium, manganese and iron. Brasses and bronzes are particularly suitable. A typical analysis of one brass matrix well suited for use in the grinding wheels of this invention for bonding the diamond grits is the following:

Element: Percent by weight Copper 70 Zinc 30 A typical analysis of one bronze matrix well suited for use in bonding the diamond grits in the wheels is the following:

Element: Percent by weight Copper 80 Tin 20 For certain applications, the hard abrasives used for the grinding of this invention can be any of those having a hardness number of at least 8, preferbaly at least 12 on the extension of Mohs scale or metal equivalent columns in the following tabulation.

(11) Fused zirconia. (l2) Fused alumina (13) Silicon carbide." (14) Boron carbide (15) Diamond (15) Cubic boron nitride (l1) Tantalum carbide (12) Tungsten carbide (9) Sapphire Diamond.

This tabulation is adapted from Ridgeway et al., Trans. Electrochem. Soc. 63, 369 (1933) by addition of cubic boron nitride at a number hardness as equivalent to diamond.

The disclosures herein of preferred diamond concentrations for the grinding, and in particular surprisingly low diamond concentrations in late stages of grinding glass are not restricted to diamond grinding of glass. These surprising results are obtained also in the grinding of various other materials, for instance stone and ceramics, with other hard abrasives such as those enumerated above having a hardness of 8 or higher, preferably 12 or higher on the extension of Mohs scale, preferably when the abrasive is used in a grinding wheel and a coolant is employed. Stone which can be ground in accordance with the present invention includes marble, granite, etc. and ceramics which can be ground include silicon carbide (Carborundum), aluminum oxide, etc.

In accordance with a still further embodiment of the invention, the surfacing of the principal surfaces, as distinct from the edges of elongated fiat sheets of glass and the like, may be accomplished by means of a rotary grinding wheel having an annular grinding face or rim with abrasive particles bonded therein, the grinding face hav ing a radial dimension of substantial extent relative to the outer diameter of the grinding wheel. As distinct from prior known methods for diamond grinding sheets of plate glass, the broad rim grinding wheel, in accordance with the invention, preferably has an annular grinding face with an inner diameter less than the breadth of the elongated sheets being surfaced, but with an outer diameter equal to or greater than the breadth of the sheets being surfaced. The novel method of surfacing the flat sheets of glass comprises the step of positioning the annular grinding face of the grinding wheel adjacent the principal surface of the sheet of glass in such relation thereto as to have at least all of the inner radial portion of the annular grinding face at all times in overlying relation to and in contact with the principal surface of the glass sheet, the control of the glass feed, the operation of the grinding wheel, and the application of coolant intromissively between the annular grinding face and the principal surface of the sheet being accomplished in a manner similar to the earlier embodiments of the invention. Comparative tests have demonstrated highly significant increases in wheel life, efliciency and other important criteria in the surfacing of plate glass by this novel method in contrast to the previous technique of employing relatively narrow grinding rims, wherein all of the grinding face passes off the surface being ground at least once, if not at diametrically opposed sectors of the surface of revolution. It was previously understood that it was necessary to have the grinding face run clear of the surface to be ground during each revolution 50 as to most effectively clear debris from the abrasive particles of the grinding face and from the surface being ground.

For a more complete understanding of the various aspects of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying figures of the drawings, in which:

FIGURE 1 is a plan view of a grooved, segmented grinding or surfacing wheel of this invention;

FIGURE 2 is a section taken on line 2-2 of FIG- URE 1;

FIGURE 3 represents an enlargement of a portion of the wheel of FIGURE 1;

FIGURE 4 is a section taken on line 4-4 of FIG- URE 3;

FIGURE 5 is a plan view of a grooved cup wheel of this invention, which cup wheel is a smaller wheel than the segmented wheel of FIGURE 1;

FIGURE 6 is an elevational section through the hollow shaft spindle of a grinding wheel of the present invention, the coolant being supplied to the inner cutting edge of the wheel through the enclosed central passageway of the hollow spindle, thi figure also showing the pump and conduit for supplying the coolant from the coolant supply tank to the hollow shaft spindle;

FIGURE 7 is an elevational section through the spindle and grinding wheel of a larger grinding wheel of the invention and showing coolant-supply orifices or holes in the wheel support, these orifices communicating with a coolant-supply conduit leading from a coolant-supply tank, thi figure also showing the coolant-supply tank and pump for supplying the coolant to the orifices and hence to the inner cutting edge of the wheel;

FIGURE 8 is a diagram representing a method of the present invention utilizing the diamond surfacing;

FIGURE 9 is a side elevational view of a single diamond grinding station for use in the present invention;

FIGURE 10 is also a side elevational view of a single grinding station for use in the method and apparatu of the present invention, the view also showing means for feeding the glass through the station;

FIGURES ll, 12 and 13 represent arrangements of segments on segment holders of grinding wheels in accordance with previous methods for grinding glass;

FIGURE 14 is a view showing an arrangement of segments on a segment holder in accordance with the present invention, the segments being in a circular arrangement and narrowly spaced from each other when mounted on the grinding wheel;

FIGURE 15 is a plan view of an alternate embodiment of the invention employing a broad rim, grooved, segmented grinding or surfacing wheel in a novel surfacing relation to the surface being ground;

FIGURE 16 is a partial radial section of the annular grinding face of the wheel in FIGURE 15, taken along the line 1616 and looking in the direction of the arrows;

FIGURE 17 is a plan view of a grinding segment forming a portion of the annular grinding rim of the wheel in FIGURE 15; and

FIGURE 18 is a partial sectional view of the grinding segment of FIGURE 17, taken along the line 1818 and looking in the direction of the arrows. 7 With reference to FIG. 1, segment holders 69 are mounted on generally circular wheel support 61. Y Segment holders 60 are plates having slightly curved outer and inner peripheral edge portions 62and 63, respectively,

with lateral edge faces 64 and 65 tapering slightly-inwardly from the outer to the inner edge. Bolts 66 and 67 are integral with the upper surface of segmentholders 60 and have threaded outer end portions, these mounting 7 bolts extending through registering orifices in the wheel support 61 to mount the segment holders securely to the wheel support with the aid of nuts on their threaded end portions.

Grinding segments 68 are secured to the lower surface or side of segment holders 69 by brazing to provide a diamond grinding plane extending generally perpendicular to the central axis of the support. As shown, segments 68 are secured to the segment holders one per segment holder. Spaced holes or orifices 69 function to discharge liquid coolant to the inner edges of grinding segments 68.

. tion in the embodiment shown in FIG. 4. These grooves together with the fine hard abrasive grits 72 of predeterm ned grit size embedded in the matrix of. these grooved cutting segments and the supply of liquid coolant to the wheel: grinding surface during the surfacing result in a significant improvement in the surfacing of the plate glass at the late stations of the grinding me-thod'of my copendmg application Serial No. 119,444, these late stations gilually employing grit sizes of 200-230 grit size and Grinding segments 68 are secured to segment holders 6!): in such manner as to cooperate with one another to form a continuous or substantially continuous narrow circular grinding face or plane located adjacentthe periphery of the wheel suport. The width of each segment of this circular arrangement is typically about 0.250 inch, and this circular arrangement of segments is located typically about 1 inch from the outer peripheral edge of the wheel support. The abrasive grits are embedded and dispersedin the matrix of each segment and as wear pro-.

' ceeds during the surfacing are exposed on the surface of the'matrix A cup-type wheel 75 is shown in FIG. 5, this wheel having radial grooves 76. As shown, cup wheeliShas 8 radial grooves each A inch wide. Wheel 75 is a 3-inch diameter wheel. Diamond grits 77 are embedded in the matrix of this cup wheel.

With reference to FIG. 8, in a specific embodiment, a sheet of plate glass, which is continuously extruded in the melting furnace, is passed through the annealing chamber in conventional and known manner. From the annealing chamber the glass sheet is passed successively ranged in members. Grinding Wheel 21 compirses a generally circular support and a plurality of grinding segments having radial grooves in the segment cutting surface as hereinbefore described and mounted on one side of the support in a generally circular arrangement adjacent the periph eral edge portion of the support as hereafter described.

Supporting frame 25 is supported by main frame 26. of

the grinding station, which also supports bearing housing 22 for the vertical spindle of grinding wheel 21. Base 27 of the grinding station pro ides a heavy rigid support for the entire apparatus." A suitable-coolant tank 28 and associated coolant pump is provided for recirculating coolant intromissively to the working surface between the grinding wheel 21 and the plate glass 15. The coolant is preferably supplied or delivered to the inner cutting edge of the grinding wheels as previously discussed, for

instance by means of'a'hollow spindle.

As'shown in FIG; 6, the coolant 1S pumped from coolant supply tank 23 by means of pump 29 through conduit f 30 into the central passageway 31 of hollow shaft spindle 32 for grinding wheel 21, passageway 31 extending along the axis of spindle SZand communicating one end of the spindle with the opposite end thereof. By reason of the centrifugal force obtaining as a result of rotation of the wheel 21, the coolant flows in an outwardly direction as indicated by the arrows to the inner cutting edge'and into contact with all of the exposed diamond grit surfaces and the surfaces of grooved grinding segments 38. As shown in FIG. 7;'with the larger grinding wheels, for instance wheels having diameter of 30 and larger, the coolant is pumped from coolant tank 43 by pump '44 through conduits 45 and 48 into ante-chambers 46 and 47 respectively which communicate with a plurality of spaced holes or orifices 4? and 50 in the grinding'wheel 51. The spaced orifices, which communicate one side of the wheel support with the opposite side thereof,,are ara generally circular arrangement adjacent and inwardly of the inner edge of the circular or generally circular arrangement-of groove diamond segments and function to discharge the coolant to the inner edge of the grinding segments 52, whereby the centrifugal force resuiting from rotation of wheel 51 causes the coolant to flow in an outwardly direction as indicated by the arrows to the inner cutting edge and into contact with all of the exposed diamond grit surfaces and the surfaces of grinding segments 52.

In the segment arrangement of FIGS. 11 and 12 the segments are not arranged in a circular arrangement on the wheel support but the segments'are at an angle to reduced in the segment arrangements of FIGS.111 and 12.- Consequently, the life of the wheel is materially shortened andfalls 0E abruptly, which is due to theexcessive pressures and stresses built up on the relatively few particles to each of one or moreinit-ial diamond grinding stations,

these initial grinding stations being typically 3 in number. Major irregularities present in the principal surface of the glass,.as distinct from the edges thereof, are substantialy removed in these initial grinding stations.

Referring now to FIGS. 9' and; 10, the sheet of plate glass 15' is'fed through an initial grinding station 16 by driving rollers 17, 18, 19 and 20' shown'in FIG. 10.

'wheel 21 is mounted coaxially ona rotatable vertical spindle contained within bearing housing 22, wheelZl being driven by motor 24 which is mounted above wheel Zlon supporting frame 25 made upof suitable supporting available at the leading and cutting edges of the segments. By the term leading edge of the wheel or segment is V meant the first edge of the wheel cutting surface making contact with the movingglass, this 'firstedge of the circular cutting surface of the wheel being the outer circumferential line of this cutting surface. By the term .trailing edge of the segment or wheel ismeant the first edge of the second half of the wheel cutting surface making contact with the moving glass, such first edge of the second half of the cutting surface being the inner circumferential line of the circular'cutting surface. The following comparative data Table I evidences the striking improvement in wheel life attained by the present invention, the wheel life being expressed in terms of cubic'inches of glass removed per carat of diamond. Data was obtained from the same Wheels as those of FIGS 1l-l4. All data were obtained under equivalent evaluation conditions.

TABLE I Segment Arrangement Wheel Life On. Surface Finish,

Inch of Glass/carat (microinches) It is readily apparent from Table I that the circular arrangement of grinding segments on the wheel support in accordance with FIG, 14, which is in accordance with the invention, gives a materially longer wheel life than is obtained using the non-circular segment arrangements of FIGS. 11, 12 and 13.

The considerable improvement in wheel life achieved by this invention is also shown by comparative data in 20-inch-by-60-inch glass specimens were -10 typical dimensions of length of 1 7 where segments are attached, width of 231 and thickness of In the initial grinding stations, the surface of the plate glass is roughly ground to remove the principal irregularities in the surface of the glass. As disclosed in FIG. 8, the diamond concentration, in terms of carats per cubic inch of wheel matrix, is relatively low in the initial stations, usually the first three stations. However, the diamond grit or mesh size should be relatively large in these initial stations. The expressions grit size and mesh size are used synonymously herein referring to particles of grits passing through sieves of the specified number of linear openings per inch. Recently sieves of good precision with openings smaller than 325 mesh have become available, and this invention includes in part the use of grits of such smaller size.

Specifically, diamond concentrations of less than 20, preferably about 9 carats per cubic inch of grinding segment matrix, may be utilized for the initial stations. The grit size is preferably about the to grit size inasmuch as the larger grit sizes, say of the order of 20 to 30, tend to cause excessive chipping of the edges of the plate glass. Further, in these initial stations, typical operating conditions are a feed speed of about 200" per minute of the glass relativeto the grinding wheel, and a cut of about .004". The grit size figures specified indicates that the diamond grits will pass through a screen of a certain mesh size but will not pass the screen of the next mesh size.

TABLE II T when we Downfeed per Table Segment Spindle Test No. Reversal Arrange- Speed Cu. in. of Cu. in. of Surface (Inches) ment, Fig. (r.p.m.) glass per glass per Finish cu. in. of carat (microdia. mat. inches) 1 Average.

As evidenced by Table H, the life of the grinding wheel is considerably longer in general, when employing the segments of the present invention as shown in FIG. 14, as contrasted with the non-circular arrangement of segments shown in FIGS. 11, 12 and 13.

Grinding segments 68, shown in FIG. 4, each have typical dimensions of length of about 1 1 width of about 0.230", and depth or thickness of about A3". The area of the grinding face of each segment 68 is'typically about 0.415 square inch. Segment holders 60 each have Thus, for'exarnple, 50 to 60 grit diamonds will pass through a 50 mesh screen but will not pass through a 60 mesh screen. The basis for mesh sizes in the present specification is the US. sieve series.

Further, as shown in FIG. 8, as the sheet of plate glass advances from the initial grinding stations to additional successive grinding stations, where additional increments of stock are removed from the plate glass, the concentration of diamonds in carats per cubic inch of wheel matrix is increased, i.e. is higher in these additional successive centrations of about 20 carats and higher, preferably lowing Table III.

face finish, and wheel life were actually measured at stations 1, 2, 3, 5, 7, 8, 1t) and 12. The data for stations 4, 6, 9 and 11 were interpolated and those fQlI StaIiQn .13 and 14 were extrapolated. The surprisingly low diamond about 20 carats per cubic inch of grinding segment matrix concentrations of the stations and 12 data were particare employed in the wheels of the additional successive ularly interesting. a

' stations. The average grit size at these intermediate or Diamond grinding 'in accordance with thlsmventlon, additional successive stations is about 100-120 grit size. as shown in Table 111, requires typically ten stages tolre- 1 Typical operating conditions in these intermediate or addiplace h n n n y-fig t n g i d g tag tional successive stations, which are usually stations No. 10 Diamond "grinding stages Nos. to. 14.replace .onthe 4-7 of th present inv io are a fe d speed f bout order of two-thirds of the conventional iron oxide or rouge 200" per minute of glass relative to the grinding wheel, p li h g g about f n adduwnal rouge stages 1 and a ut of bo t ,002", i V accordance with conventional methods for; f nal polish- As shown in FIG. 8, the glass sheet is then advanced g of p a g a a ic n after e fourteen iamon to the later or late grinding stations/these late grinding 5 g g Stagesl stations usually being stations No. 844. It is found that T n le reduction i diamond eq m n employment of low concentrations of diamond grits in for the Whfiels 0f the a stations i readily pp en these later or late stations materially lower than employed from the data- Of Table the w of t st ti n in the additional successive stages, with the grits substan- Iii-14 aving optimum diamond concentration f f tially uniformly dispersed and bonded in the grinding ly 1 Carat P cubic inch of matrix. dawn i 5 10W segment matrix, gives excellent grinding results with a as .05 carat per cubic inch of matrix as contrasted with striking economy in'diamond requirements and a considthe wheels of initial stations 1-3 and additional successive erable reduction in surfacing costs- The use of these lower stations 4-7 havingv a lcolisidfifflbly higher diamond C concentrations of diamond grits with good results in the centration. Concentrations 'of diamonds as low-as .05 7 late stations is directly contra to what was previously carat per cubic inch and even lowerfcan be. used with believed. Diamond concentrations which can be mates satisfactory results in the wheels of the late stations in rialiy lower than 9 carats, preferably lower than 1 carat. accordance with this invention. In connection with these per cubic inch of grinding segment matrix, are employed late stations, it was found to be of the utmost importance in the wheels of these late stations. This reduction in to :control within close limits the number or concentrationv diamond requirements can be readily seen from the folof diamond grits in the leading and trailing edges of the wheel.

TABLE III Typical plate glass grinding with diamonds Diamond Optimum surraee Wheel Life Station Concentra- Width of Glass Finish N o. Grit Size tion in Car- Cutting Face Removal (Microats/In. of Wheel (Mils) inches) Ft? of 111. of

(Mlls). Glass/Carat Glass/Carat -60 9 6 V 220 5,200 3,000 7 50-60 9 V 4 220 5, 200 3,000 V 7 .50- 9 4 220 5, 200 3, 000 -80 15 3 140-170 6, 900 -120 20 2 90-110 10, 400 3, 000 -140 16 1. 5 70-90 13, 300 3, 000 -170 12 l. 3 60-70 16, 800 3, 000 200-230 9 1. 0 40-50 20, 800 3, 000 270-325 5 r 0.75 25-35 29, 700 3, 000 500 1 0. 5 12-20 41,600 850 0. 6 0. 25 8-12 83,300 3: 000 l, 050 0.2 0. 2 6-8 104, 000 3,000 1,250 0. 1 0.15 4-6 139,000 3, 000 2, 500 0. 05 0. 1 7 2-3 208, 000 3, 000

In the tests of Table III a 3-inch outer diameter cup wheel was used (actually 2 Aa-inch outer diameter of the grinding surface). 2-inch-by-18-inch glass specimens were moved reversibly in the long direction at a feed speed of 200 inches per minute. Coolant concentration and flow rate were maintained constant during the periods of the tests.

In each casenew polished plate glass was used for a test. However, it is believed that late station grinding of glass previously ground with coarser grit diamonds would generally afford longer wheel life, require less spindle power, and give operation with less'tendency to glass breakage; thus, all wheel life figures in Table III for the late stations'must be considered conservative.

As regards the data presented in Table III, the-data given for optimum width of cutting face of wheel, surstation 5, for 200-230. grit size diamonds used for station 8, for 500 grit size diamonds used for station 10, and 1050 grit size diamonds used for station 1;.

l Downleed.004 per table reversal. Coolant Cone.50:

TABLE IV Efiect-of varying diamond concentration on wheel performance (All tests at table speed of 200 per minute. 3 outer diameter cup wheels used.)

Diamond Average Glass Preferred Concen- Wheel Lite Net Surface Breakage Diamond Grit Size tration (Carats/ Spindle Finish (MW thick Sequence Concen- (Carats/ cu. in. of Power (Mieroglass) of Tests tration cu. in. of glass) (Watts) inches) (percent) Range matrix) 6 680 500 310 7. 2, 090 707 229 0 9 2, 561 723 230 0 7. 5 to 18 18 2, 624 1, 150 162 40 36 100 2 F iii 33 3 3 1, 067 197 74. 2 0 s a: a

3 3, 216 570 18 0 6 1, 403 725 21 0 5 to 9 9 1, 041 854 25 20 20 621 768 29 40 68 1, 250 33 100 60 2 Excessive 100 Dorvnfeed.002 per table reversal. Coolant Conc.25: 3 Downieed.001" per table reversal. Coolant Cone-25:1.

4 DoWnieed-.0005 per table reversal. Coolant Cone.25:1. Diamonds in 30 to 50, size range. 5 Downieed.0002 per table reversal. Coolant Cone-25:1. Diamonds in 8 to 2511 size range.

The Table IV data shows a relatively narrow preferred diamond concentration range for 60 grit diamonds of 7.5 to 18 and somewhat broader satisfactory concentrationresults for additional grinding with smaller sized grits. Thus, for 100-120 grit size satisfactory grinding took place at 15 to diamond concentration but not at 9. diamond concentration, for 200-23O grit size satisfactory grinding took place at 5 to 50 diamond concentration but not at 70 diamond concentration, and for 500 grit size favorable grinding took place at .5 to 9 concentration, unsatisfactory grinding at 20 concentration, and extremely bad operation at 40 and 60 concentration. For 1050 grit s ze, favorable grinding took place at the remarle ably low diamond concentration of .05 to 3 carats per cubic inch.

For the 200-230 gn't size and 500 grit size diamonds the sequence, in which the tests were run is given. The order of the experiments shows how completely unexpected were the superior wheel performance results with low diamond concentrations at the late stations. 7

With any particular size grit the type of diamonds and wheel construction methods were kept identical for all diamond concentrations, so that for each size the results for difierent concentrations are completely comparable.

It will be understood that grinding of glass as delivered from the melting furnace and rollers is referred to in the data shown in Tables III and IV. In general, the number of stages necessary for grinding of any material depends on the initial roughness of its surface. For material with smoother surface than glass from the melting furnace, the initial stages described in Table III will be unnecessary and may be omitted. For example, if it is desired to convert sheet glass to plate glass by a glass removal of 5 to 10 mils (rather than approximately 25 mils as used according to TableIII), the first 4 or 5 stations of Table III may be omitted and glass with a surface finish of 2 to 3 microinches may be obtained by following the teachings of this table regarding the other stations. The minute diamond concentrations indicated in'Ta'bles III andIV, especially of the relatively small 1050 mesh grits evidence High stresses are produced in the the striking reduction in diamond requirements and considerable reduction in grinding costs achieved by the present invention.

The diamond concentrationsdiscussed apply for any annular width of the grinding surface on the wheel, for example, a width of to 12", provided essentially all of the circumference of the wheel contains a diamond grinding surface. With conventional wheel making procedures a width of about A" is preferred. Special large diameter wheels, for example, 12 feet in diameter, with greater widths of the grinding surface, can be made in accordance with the principlesof the invention.

Referring again to FIG. 8, from the diamond grinding stages, the plate glass sheet is then advanced to iron oxide or rouge polishing stations, where it is polished in conventional and known manner. The polishing heads at the polishing stations also have vertical spindles and iron oxide or rouge is employed asan abrasive. By virtue of the present invention, the number of iron oxide polishing stations required is reduced or lowered considerably as contrasted to the 42 polishing stations previously required. After completion of the grinding and polishing of one side of the plate glass, the plate glass is reversed or turned over, blocked and passed through the second side diamond grinding stations and iron oxide polishing stations, also shown in FIG. 8, and similar in structure and number as those employed for grinding and polishing the first side. The grinding and polishing of both sides of the plate glass sheets are then completed.

As pointed out in copending application Serial No. 50,352, filed August 18, 1960, basic variables involved in glass grinding with diamond grinding wheels include the rate of feed conveyor speed for the plate glass sheet being ground, and the rate of rotation of the diamond grinding wheel. The conveyor speed or rate of feed of the glass is normally given in terms of inches per minute. Conveyor speeds of 200 inches per minute and higher are practical in the present invention. However, lower speeds of about 175 inches per minute and lower can also be employed. The rate of rotation of the diamond grinding wheel in terms of revolutions per minute is not particularly significant, as the rate or speed at which the grinding surface engages the plate glass is also dependent on the radius of the wheel. With the diamond grinding surface being concentrated near the outer periphery of the grinding wheel, a more useful value is the rate at which the diamond grinding surface passes over and engages the plate glass, in terms of surface feet per minute. This is equal to the circumference of the wheel multiplied by the number of revolutions per unit time of the wheel. Thus, with'a wheel having a diameter of about 10 feet, the rate of rotation is about 90 to 95 revolutions per minute in order to produce a relative velocity between the glass and the diamond grinding surface of about 2800 or3000 surface feet per minute. The stress produced in the glass during the grinding is also a factor of importance, inasmuch as chipping or breakage of glass resulting from high stresses cannot be tolerated to any significant extent. glass with attendant glass chipping or breakage by use of excessively high diamond concentrations when large amounts of stock are to-be moved at initial stationsiin'the grinding process. Use of diamond particles sizes which are too large also results in chipping or breakage of the glass. Further, use of lean coolant concentrations are accompanied by an increase in the grinding stresses. The spindle power which is absorbed is indicative of the stresses, and the likelihood of. glass chipping or'breakage.

The diamond grinding wheels of this invention can have a circular or generally circular wheel support as large as 2 feet, 12 feet, or larger diameter.

There appears to be at all the stages in the diamond grinding of plate glass an optimum pressure for each diamon-d particle, decreasing with decrease in the average diamond particle size, Thus, the invention makes posbonded in the wheel matrix,

sible, based on the relationships found between number of diamond particles and their size, a calculation (borne out experimentally) for the preferred diamond concentration in carats per cubic inch for any useable grit size of diamond wheel. a

The preferred number of diamonds and diamond concentration will vary somewhat depending on the pressure applied in the grinding. Thus, a somewhat higher spindle power is acceptable resulting from a higher concentration of diamonds, for example, when relatively thick glass is used.

The term diamonds or diamond is used herein in a broad sense to include both natural diamonds and synthetic diamonds having the approximate hardness or other abrasive qualities of natural diamonds" Diamond concentrations have been given in carats per cubic inch, with the carat, which is equal to one-fifth of a gram, being the usual unit of diamond weight. With other abrasives which are not of gem quality, it is regarded as suitable to express concentrations as grams per cubic'inch'.

In honing surfaces and/or edges ofmaterials' 'in'fa'ccordance with this invention, the surfaces and/ or edge of the material is ground with'a grinding wheelhaving'a low concentration of hard abrasive grits bonded. the grinding surface of the Wheel matrix. The abrasivegrits are those characterized by having a'hardnefs's of'8 or higher, preferably 12 or higher on the extensionofMghs scale, such as diamonds and cubic boron nitride. The materials which can be honed include metals, for instance, ferrous metals, e.g. iron and steels, stone, glass, ceramics, and cemented carbides. The edges of these materials which can be honedinclude the edges immediately adjacent and defining holes or orifices. When using a grinding wheel for the honing having diamond grits low concentrations of diamonds of less than 2 carats per cubic inch. ofrfn'atrix can be used. By the term honing used herein is meant converting a non-smooth a smooth even surface or edge, substantially free of irregularities. Honing includes the sharpening of edges of materials, for instance the edges of metallic objects, e.g. ferrous metal cutting blades.

The following examples further illustrate the invention. In all of the examples the grooves were wide and positionedradially at approximately even spacings on the cutting surfaces of the wheels.

For example, the number and disposition of grooves used may be: 1

Four-V wide radial grooves at intervals in the cutting surface of the wheel.

Eight fl wide grooves as above, at 45 intervals.

Sixteen- A wide grooves as above, at 22V2 intervals.

Thirty-two% i Wide grooves as above, at 11 A intervals.

Forty-Eight wide grooves as above, at 5% intervals.

Ninety-sin- A wide grooves as above, at 2 inter:

vals.

The grooves extended from the inner to the outercircumference of the cutting surface. New'polished glass was used for each test. In each test of Examples}, H and III the table speed was 200 inch/minute andthe 001 ant flow rate was maintained at 3 .0 gals. pe'r'rniniitefl EXAMPLE I without grooves in the tables.

or irregular surface or edge: into TABLE V 1050 grit size (8-25 micrns)3" 0.D. wheels Diamond Wheel Face Diamond Net Spindle Average Concentration Downfeed Width Life (Carat! Power Surface (Carats/cu. in.) (Inches) (Inches) cu. in. oi (Watts) Finish glass) (Microinches) 1 Four Ms Radial Grooves in Wheel Cutting Surface. 2 Eight Ms" Radial Grooves in Wheel Cutting Surface.

Average.

The data in Table V show that under comparable conditions, for diamond concentrations of 1.5 and 0.5 carats/ cu. in. the insertion of four 95 wide grooves more than doubled the diamond life of these wheels. At diamond concentrations of 0.25 carat/cu. in. without grooves, the wheels could not be operated at nominal downfeeds without excessive burnishing. However, with grooves as described herein, the diamond life of the wheels was typically over 3000 cu. in. of glass/ carat at a downfeed of 0.0002".

Comparative performances of wheels with and without grooves for 3'' OD. 500 diamond grit wheels are given in Table VI. The grooved wheels had four 4 wide radial grooves spaced at 90 intervals.

TABLE VI 500 grit size (-50 micr0ns)3" 0.D. wheels Spindle speed=3600 r.p.m. Glass specimens=2' x 18 Downfeed=0.0005"/table reversal Diamond Wheel Face Diamond Net Power Average Sur- Concentra- Width Life (Carat/ Spindle face Finish tion (Carats/ (Inches) cu. in. 0! (Watts) (Microcu. in.) glass) inches) 1 No radial grooves in wheel surface. 2 Average.

The diamond concentration on all wheels was 1.5 carats/cu. in. which was evaluated as the optimum diamond concentration.

The data of Table VI confirms the statement of Example I that a diamond life of over 3000 cu. in. of glass/ carat is possible with all grit sizes from 5.0/ 60 to 1050.

EXAMPLE H The purpose of this example is to show the efiect of the number of grooves on the performance of a surfacing wheel. The data in Table VII are for a 3" OD. wheel of 0.250" wheel face width, containing 1500 grit (6-10 micron diamond powder) at 0.25 carat/cu. in. concentration. After testing the wheel with 8 equally spaced grooves with unsatisfactory operation, additional grooves were cut to give 16 grooves, followed by sufficient testing to obtain the result indicated. Additional grooves were then cut on the same wheel to obtain the 32-groove results.

l Optimum No. of Grooves.

From the data in Table VII it can be seen that the Wheel with 16 grooves was superior to that with 8 grooves and 32 grooves.

EXAMPLE III The purpose of this example is to show the relationship between the number of grooves used for satisfactory performance and the grit size for wheels of a given size.

TABLE VIII Diamond life and surface finish for 3'' OD. grooved diamond wheels Diamond Optimum Approx. Diamond Liie Concentra- No. of M6 Downfeed Wheel Face 7 Net Spindle Surface Grit Size tion (carts/ Radial (inches/table Width Power Finish 7 cu. in.) Grooves reversal) (Inches) cu. in. of Sq. Ft. of (Watts) (Microinch'es) glass/carat glass/carat In Table VIII the performance of the grooved wheels The 18" glass specimens used with the 3" wheels is a with various grit sizes'is given. The optimum number closer approximation of the continuous glass application of grooves is given for each grit size. The data in this but is still a conservative estimate.

table show that as the grit becomes finer, a larger num- When used in a 30" Wheel, a 60" specimen of glass ber of grooves is necessary. would be equivalent to a 6'. specimen of glass usedwith All wheels shown in Table VIII contain the same I a 3" wheel. A diamond life 'of only 1600 cu; in. ofgla'ss bond. 7 The 1500 grit wheel disclosed therein shows a 20 per carat was obtained using a specimen of glass 6" long considerably higher diamond life in carats per cubic inch with a 3" 0.13. wheel. However, if a specimen of glass of glass than the 1500 grit wheel disclosed in Table VII. 18" long is used with a comparable 3 wheel, a diamond This difference in performance is believed due to a dif- Wheel life of over 3000 cu. in. of glass per carat can be fercnce in the wheel bond used. 7 obtained. r 7 It should be noted that a diamond life of 1650 cu./ in. Based on evaluation of wheel life with glass specimens of glass/carat for agrit size of 1500 (6-12 microns), deof various lengths, it has been found that a 1219 cu; in. spite being less than the glass removal for coarser grit, is of glass/carat diamond life with a 60" specimen in a favorable. The demonstrated finishing of 115,000 sq. wh l wo ld be equivalent to a diamond life of overft. of glass/carat with 1500 grit wheels indicates that n 3000 cu, in. of lass per carat if the wheel were operated such wheels are economic. V with continuous glass lengths.

- I The data in Table 1X show that the number of grooves P needed for favorable performance of the 30" wheels The Pu p O this example 15 to Illustrate the P increases as the grit becomes finer. Comparing the data ance of 30" diamond, l ffiamcnd life F in Table 1X with that in Table VIII, it can be seenthat and surface finish of the wheels is given 1n Table 1X. using 500 grit Whaels at a diamond concentration Oi 15 these tests 0 2, 3 P F Q w used 9 carats per cu. in., the 3 wheel having 4. grooves produced the wolant was ar t approxlmatelv 100 s a diamond'life' of over 3000 cu. in. of glass per carat and ute. 1 a surface finish of 19 mieroinches, and the 30"wheel In evaluating the data of Table h diamond m having 96 grooves produced comparable results. of 1,219 for the 500 .gri't9 6 groove wheel is equivalent to 40 TABLE IX Performance of diamond wheels-Approx. 30" OD.

Table speed=200 inches/min. Spindle speed-=370 r.p.m.

Diamond Downfeed Aprox. Diamond Surface Grit Concentra- No. of 1 Me (inches/table Wheel Face Lite (cu. in. of Net Spindle Finish Size tion (carats! Grooves reversal) Width glass/carat) Power (KW) (Microinches) cu. in.) (Inches) I 1 The wheels were assembled from 48 segments, and the segments were assembled to butt closely together making a continuous peripheral wheel. Me grooves were inserted'where the segments articulated. .For96 grooves, one additional M6 groove was lnserted 1n each segment.

2 Average 0M tests.

adiamond life of over3000 cu. in. of glass per carat in In accordance with the still further embodiment of h t 011 Wheels i g X 8 .358 SPeCithe invention in FIGS. 15-18, a rotary grinding'wheel mens. V 8,0, in contrast to the specific embodiment in FIGS. 1-4,

The controlling factor was the length of the glass for example, has a broad grinding face or rim 8'1, havpe me r lative to the size of the Wheels. It has been ing a substantial radial dimension relative to the outer found that glass specimen length has a considerable eifect diameter of the grinding wheel 80. The annular grindupon the diamond wheel performance. In testing the ing rim 81 comprises two concentric rings each having a performance of the wheels, with each table reversal the plurality of contiguous arc'uate segments 82 and 83sepwheel goes 01f the glass completely. During the going arated by a concentric groove 84, in which is disposed off and coming on stages abnormal pressures are exerted a plurality of angularly displaced mounting means such on the cutting wheel surface. Such pressures have been as the bolts 85 and a locking strip 89, of any suitable found detrimental to the wheel performance. This .probconventional form, for securing the plurality of segments 7 lem would obviously not be present where continuous 82 and 83 to the grinding Wheel support 86.

glass lengths are used, but i's'characteristic of the labora- V a Each of the arcuate' segments 82 and 83 comprises toryequipment used in these tests. a suitable matrix having a predetermined concentration The 60 glass specimen length. used routinely in tests of abrasive grits bonded therein and secured'to segment with 30" wheels does not simulate the continuous glass holders 87 in a manner similar to the-mounting of the length of" the ultimate plate glass surfacing very well. grinding segment 68 in the Wheel of FIG. 1. The annular grinding rim 81 may comprise a single broad rim, either unitary or segmented.

Each of the arcuate segments 82 and 83 has a plurality of radial grooves 90 formed therein in any suitable manner to facilitate the passage of coolant, as discussed in greater detail with respect to the previously disclosed embodiments of the invention. Each of the radial grooves 90 in the segments 82 and 83 communicates with the concentric groove 84. In some circumstances, it may be desirable to utilize a plurality of concentric grooves similar to that shown in FIGS. and 16, intermediate a greater plurality of concentric rings of arcuate segments and even concentric grooves formed within the faces of the arcuate segments 82 and 83 in a manner similar to the formation of the radial grooves 90. Branching and multiple branching of the inner radial grooves in one or more inner concentric rings of the annular grinding rim may still further facilitate and promote the most eflicient distribution of coolant.

Coolant of a suit-able concentration such as parts of water to 1 part of oil and emulsifier may be supplied to the grinding wheel 80 in accordance with the methods of FIG. 6 or 7 or any other suitable method of coolant distribution. Further, apertures for intromissively supplying coolant to the grinding face of the grinding wheel 89 may be located in the concentric groove 84 to assist and further promote the most eflicient supply of coolant to the grinding face, bearing in mind that, because of the rotation of the brinding wheel, the coolant will flow outwardly across the grinding face under the influence of centrifugal force.

The radial grooves 90 and the concentric groove 84 are preferably flat bottomed grooves of uniform width so that the groove width does not change as the grinding surface wears away. Fru ther, as is seen in FIGS. 17 and 18, the radial grooves 90A at the edges of the segment 82 are laterally open grooves of a Width half that of the interior grooves 90, so that the groove formed by contiguous grooves 90A of abutting segments 82, or similarly of segments 83, have the same width as the interior radial grooves 90.

In one exemplary embodiment using a plurality of grinding wheels constructed in accordance with the invention as disclosed in FIGS. 15-18, the outer diameter of the grinding wheel 80 is 5 feet, the breadth of the annular grinding face, i.e. the radial dimension across radially disposed adjoining segments 83 and 82 and the intermediate concentric groove 84 is 13 inches, including a radial dimension of 5 inches for the segment 83, 1 inch for the concentric groove 84, and 7 inches for the segment 82. The radial grooves are on the order of A1 inch in depth and inch in width, there being 15 grooves per segment. The sheets of glass being ground are carried in beds of plaster of Paris on a series of cars some twelve feet in length abutting each other in a continuous train with plaster of Paris filling in gaps between successive sheets to present a continuous surface.

In contrast to the specific embodiments disclosed previously in this application and my other co-pending applications, and in fact to any known methods of diamond grinding plate glass, for example, it has been found that there is a critical relationship between the broad annular grinding face and the breadth of the sheet of glass being surfaced. Previously it has been customary and considered necessary to have the full breadth of the grinding rim clear the surface being ground at least' once each revolution. However, tests conducted in accordance with the invention 'have demonstrated that there is a striking and highly unexpected increase in wheel life and overall efficiency, and improvement in surface finish when at least all of the inner radial portion of the annular grinding face is at all times in overlying relation to and in contact with the principal surface of the sheet of glass. In accordance with this novel process, the dimensions of the grinding wheel and its annular grinding face relative to the surface to be ground must be such that the inner diameter of the annular grinding face is less than the breadth of the sheet of glass being surfaced, and the outer diameter is either equal to or greater than the breadth of the sheet being surfaced.

For example, in FIG. 15, the grinding wheel having an outer diameter of 5 feet is illustrated in grinding relation to a continuous strip 92 of glass having a breadth of 4 feet.

One or more broad rim grinding wheels constructed in accordance with the invention may be readily substituted for some or all of a much greater plurality of conventional loose abrasive grinding stations in a commercial surfacing line with a coincident reduction in the number of required conventional polishing stations, the diamond concentrations and particle sizes of the respective grinding wheels being progressively proportioned in accordance with the disclosure of this application or my earlier copending applications.

By utilizing broad rim diamond grinding wheels wherein at least all of the inner radial portion of the annular grinding face is at all times in overlying relation to and in contact with the sheet of glass being surfaced, as few as four diamond grinding stations with respective diamond concentrations progressively in the order of 3, 4, l, and 0.75 carats per cubic inch and diamond particle sizes progressively decreasing from 250-297 microns to 1020 microns, at a line speed of some 30 inches per minute can produce a surface finish of 2.0 microinohes by an overall glass removal of .0376 inch to enable the production of plate glass having a substantially optical quality and a strength not heretofore normally realized following the application of conventional grinding techniques. Similar results can be obtained at higher line speeds by adding additional grinding wheels of similar construction but with appropriate changes in diamond grit size and concentrations, in accordance with the invention.

As is evident from the aforementioned example, the broad rim method of the invention accomplishes a strikingly improved surfacing and surface finish with a substantial and highly significant reduction in the number of required diamond grinding stations of the earlier forms of the invention.

Thus there is provided in accordance with the inven tion, novel and improved grinding apparatus and methods of operation capable, for example, of surfacing large elongated fiat sheets of glass and the like with substantial economy over prior known methods of plate glass surfacing to obtain substantially improved quality of surface finish.

It will be obvious to those skilled in the art that the above described exemplary embodiments both as to method and apparatus are susceptible of modification and variation without departing from the spirit and scope of the invention. For example, while the embodiment of FIG. 8 calls for a plurality of initial grinding stations and similar pluralities of additional and late grinding stations, in practice it may be found satisfactory depending on the nature of the surface being ground, the dimensions of the grinding face, the nature and concentration of the abrasive and other factors that only one wheel instead of a plurality maybe required to effectuate the initial, additional, or late grinding stages. Further, satisfactory processing or surfacing may be accomplished under some circumstances by omitting the initial grinding station or stations having a low concentration of abrasive. Therefore, the invention is not deemed to be limited except as defined by the depending claims.

I claim:

1. A process for the surfacing of the principal surfaces of a fiat sheet of glass and the like, the principal surfaces being of a predetermined breadth, by means of a rotary grinding wheel having a substantially continuous annular grinding face with abrasive particles of a grit size not greater than 200230 grit size bonded therein, the grinding face having a radial dimension of substantial extent relative to the outer diameter thereof, the inner diameter of the annular grinding face being materially less than the breadth of the sheets being surfaced, comprising the steps of positioning the annular grinding face of the grinding wheel adjacent a principal surface of the sheet of glass being surfaced in such relation thereto as to have at least all of an inner radial portion of the annular grinding face at all times in overlying relation to and in contact therewith, feeding the sheet of glass past the grinding Wheel to effect surfacing the principal surface thereof, rotating the grinding Wheel at a predetermined rate, controlling the doWn-feed of the annular grinding face upon the principal surface of the sheet, and supplying a coolant for intromissive flow in a predetermined distribution intermediate the annular grinding face and the principal surface of the sheet. 7

2. A process for the continuous surfacing of the principal surfaces of an elongated flat sheet of glass and the like, the principal surfaces being of a predetermined breadth, by means of a rotary grinding wheel having a matrix forming a flat substantially continuous annular grinding face with abrasive particles of a grit size not greater than 200-230 grit size bonded therein, the grinding face having aradial dimension 1 of substantial extent relative to the outer diameter thereof, the outer diameter of the annular grinding face being equal to or greater than the breadth of the elongated sheet being surfaced and the inner diameter of the annular grinding face being materially less than the breadth of the elongated sheet, the annular grinding face having a plurality ofradial grooves formed therein to facilitate the distribution of coolant, comprising the steps of positioning the annular grinding face of the grinding'wheel adjacent a principal surface of the sheet of glass being surfacedin such relation thereto as to have at least all of an inner radial portion of the annular grinding face at all times in overlying relation to and in contact therewith, feeding the sheet of glass past the grinding wheel at a predetermined speed .to effect surfacing the principal surface thereof, rotating the grinding wheel at a predetermined rate, controlling the down-feed of the annular grinding face upon the principal surface of the sheet, and supplying a coolant for intromissive flow intermediate the annular grinding face and the principal surface of the sheet to produce a predetermined distribution of coolant flow across the grinding face in engagement With the sheet.

3. A process for the continuous surfacing of the principal surfaces of elongated flat sheets of glass and the like, the principal surfaces being of a predetermined breadth by means of a rotary grinding wheel having a matrix forming a flat substantially continuous annular grinding face with diamond particles of a grit size not greater than 200-230 grit size bonded therein in a concentration not greater than 9 carats per cubic inch, the grinding face having a radial dimension of substantial extent relative to the outer diameter thereof, the outer diameter of the annular grinding face being equal to or greater than the breadth of the elongated sheet being surfaced and the inner diameter of the annular grinding face being materially less than the breadth of the elongated sheet, the annular grinding face having a plurality of radial grooves formed therein to facilitate thedistribution'of coolant, comprising the steps of positioning the annular grinding face of the grinding wheel adjacent a principal surface of the sheet of glass being surfaced in such relation thereto as to have at least all of an inner radial portion of the annular grind-ing face at all times in overlying relation to and in contact therewith, feeding the sheet or glass past the grinding Wheel at a predetermined speed to effect surfacing the principal surface thereof, rotating the grinding wheel at a predetermined rate, controlling the do'wn-feed of the annular grinding face at a V predetermined rate upon the principal surface of the sheet to maintain a predetermined pressure and relation between the diamond particles and the surface being ground, supplying a coolant having a predetermined concentration of parts of oil and emulsifier to water for intromis sive flow. intermediate the annular grinding face and the principal surface of the sheet, and producing a predetermined substantially uniform distribution of coolant flow through intercommunicating fluid flow paths including the radial grooves across the grinding surface in engagement with the sheet to facilitate and promote an efficient distribution of coolant with respect to all of the diamond particles exposed in grinding relation to the sheet.

' References Cited by the Examiner UNITED STATES PATENTS 1,583,807 5/1926 Soderberg 51110 2,733,552 2/1956 Rundbiad 'et'al. 51-110 f 2,944,374 7/1960 Persson 51,110 2,922,264 1/ 1960 Mushrush 51 -281 2,985,989 5/1961 Knost 51-110 3,067,551 12/ 1962 Maginnis 51--281 ROBERT C.VRIORDON, Primary Examiner. LESTER M. SWINGLE, Examiner. LEONARD s. SELMAN, Assistant Examiner. 

1. A PROCESS FOR THE SURFACING OF THE PRINCIPAL SURFACES OF A FLAT SHEET OF GLASS AND THE LIKE, THE PRINCIPAL SURFACES BEING OF A PREDETERMINED BREADTH, BY MEANS OF A ROTARY GRINDING WHEEL HAVING A SUBSTANTIALLY CONTINUOUS ANNULAR GRINDING FACE WITH ABRASIVE PARTICLES OF A GRIT SIZE NOT GREATER THAN 200-230 GRIT SIZE BONDED THEREIN, THE GRINDING FACE HAVING A RADIAL DIMENSION OF SUBSTANTIAL EXTENT RELATIVE TO THE OUTER DIAMETER THEREOF, THE INNER DIAMETER OF THE ANNULAR GRINDING FACE BEING MATERIALLY LESS THAN THE BREADTH OF THE SHEETS BEING SURFACES, COMPRISING THE STEPS OF POSITIONING THE ANNULAR GRINDING FACE OF THE GRINDING WHEEL ADJACENT A PRINCIPAL SURFACE OF THE SHEET OF GLASS BEING SURFACED IN SUCH RELATION THERETO AS TO HAVE AT LEAST ALL OF AN INNER RADIAL PORTION OF THE ANNULAR GRINDING FACE AT ALL TIMES IN OVERLYING RELATION TO AND IN CONTACT THEREWITH, FEEDING THE SHEET OF GLASS PAST THE GRINDING WHEEL TO EFFECT SURFACING THE PRINCIPAL SURFACE THEREOF, ROTATING THE GRINDING WHEEL AT A PREDETERMINED RATE, CONTROLLING THE DOWN-FEED OF THE ANNULAR GRINDING FACE UPON THE PRINCIPAL SURFACE OF THE SHEET, AND SUPPLYING A COOLANT FOR INTROMISSIVE FLOW IN A PREDETERMINED DISTRIBUTION INTERMEDIATE THE ANNULAR GRINDING FACE AND THE PRINCIPAL SURFACE OF THE SHEET. 